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The Advanced Dinosaur Egg Guide
Please share this with those who have egg questions. When possible, technical terms were avoided or defined. Every effort has been made to ensure accuracy, but it is always important to do your own research. This guide is merely a snapshot of information taken from many scientific publications. I am not an expert on eggs, rather I just love sharing what little I have learned over the years, what science has learned over the years.
For an overview on how to spot a fossilized dinosaur egg and the sizes of eggs, see the basic guide:
Somewhat outdated yet still a good overview of dinosaur reproduction and eggs, with a focus on Mongolia:
What is so special about eggs?
The amniotic egg is one of the most significant evolutionary adaptations as it allowed vertebrate life to permanently exist on land. Long before the dinosaurs and their modern descendants including the chicken, the egg came first. In fact, the better question to ask is “Which came first? The lizard or the egg?” Before the amniotic egg, amphibians and some fish were the only vertebrates able to even venture on land and only for rather short periods of time.
A great deal of information has come from studying eggs. What we have learned is summarized as:
From University of California Museum of Paleontology
Egg Anatomy:
Using the best known modern avian dinosaur, the chicken--scientifically Gallus gallus, let us go over the different parts of an egg:
“(A) The generalized anatomy of an egg. (B) The chicken eggshell comprises three crystalline layers, including the mammillary layer, prismatic layer, and external layer. The cuticle layer overlying the calcareous eggshell is further divided to two layers, including a HAp inner layer and a proteinaceous outer layer. The shell membrane, namely membrane testacea, is also characterized by two layers. (C) SEM image of the cuticle on the surface of the Gallus eggshell, showing a patchy and cracked pattern. (D) SEM image of the radial section of the Gallus eggshell. The white arrow indicates the cuticle layer that lies on the calcitic eggshell.” From Yang et al. 2018 Fig. 1
Those were technical terms, so how about we simplify. The chicken egg has three distinct shell layers mainly made of calcite, then a soft membrane on the inside of that. What is known as egg whites are the albumen which surrounds the yellow yolk located near the center. The embryo develops within the albumen and is fed with nutrients stored in the yolk. The surface of eggshell is full of openings, tiny pores, and these allow for gas to pass through the shell. A developing embryo needs to breathe just like any animal.
Additional information:
http://www.ucmp.berkeley.edu/science/eggshell/eggshell1.php
How to spot a fake egg:
First, the best way to avoid fake eggs is to go and collect them yourself. Always make sure to follow the laws and have permission to collect. In the United States, typically a good way to follow the law is through collection on private land with expressed permission from the landowner. Views of paleontologists do range on private ownership of fossils with many not condoning or endorsing. I personally have little issue with it since amateur collectors have made countless important finds while prospecting for their personal collection. If you are going to buy, do everything possible to ensure the egg or any fossil was legally collected.
Often with fake eggs everything seems too perfect. Eggs are delicate and easily crushed or damaged so if there are no signs of any damage or natural alterations be very wary. If the surface has ridges, check to see those ridges continue across a crack or break of the shell. Many fake eggs are mosaics made up of real eggshell fragments assembled together in an egg shape. These mosaics tend to not have the eggshell match on opposite sides of a crack. If you would like more information beyond what is provided or have an unanswered question, feel free to start a thread. If after reading, you want to purchase an egg then please ask the seller for the best pictures they can provide of that egg with something to show scale such as a ruler and start a thread. There are many on the forum who are happy help determine if an egg is in fact real.
Just please, whether collecting or buying, make sure you know the laws and follow them.
A few good threads on real vs fake eggs:
http://www.thefossilforum.com/index.php?/topic/69391-examples-of-commonly-faked-dino-eggs/
http://www.thefossilforum.com/index.php?/topic/83533-red-flag-on-hadrosaur-egg/
http://www.thefossilforum.com/index.php?/topic/71462-beware-of-hadrosaur-eggs/
http://www.thefossilforum.com/index.php?/topic/79465-this-is-how-realistic-a-fakereplica-oviraptor-egg-looks/
How are eggshell and eggs classified?
Many people try to name an egg to a specific dinosaur, usually incorrectly. With embryonic remains, however, an egg can be scientifically linked to a particular dinosaur (explained in the next section). Another accepted way for eggs to be linked is through a pregnant female, there are examples of females which died while carry eggs internally. Adults on top of a clutch can be used however only with caution. Eggs are given their own naming scheme just as animals have theirs.
In normal taxonomy, we have species, genus, and family whereas eggs have an oospecies, oogenus, and oofamily. The term used for egg taxonomy is parataxonomy. Parataxonomy is used in place of traditional taxonomy when an actual animal or plant cannot be linked, for example--from a lack of data. In the case of Troodon formosus, its eggs are the oofamily Prismatoolithidae, oogenus Prismatoolithus, and oospecies levis. Parataxonomy is the same system used for trace fossils, such as footprints which are normally not linked to the dinosaur who made them.
What is inside a fossilized egg?
Is there a yolk? What about bones?
Very rarely are embryonic bones found, typically eggs have been filled in with sediments. These then lithify (become rock) and so the inside of nearly all fossil eggs is rock that is similar, if not identical, to the surrounding rock. Eggshell is brittle by its nature and so often cracks, these cracks allow whatever sediments are surrounding to fill in the egg and, depending on how recent it was laid to said crack, allow the amniotic sac and other fluids to drain out.
Here is a CT scan of some eggs I am working on. You can see how the surrounding rock is very similar to the inside of the eggs.
In addition to looking for embryonic material, the scan gives us information on the infill, the true shape of the eggs, and reveals anything which could otherwise not be seen within them. Sometimes insects can be found near an egg, for example.
Embryonic bones from the oviraptor Citipati, this embryo is curled within the egg.
From Wikimedia Commons
Importance of Embryonic bones:
https://youtu.be/cubdagTiRHE?t=48
Embryonic remains are vital for an actual animal ID, so any chance of them being present must be investigated. If you have any tiny bones which can be seen inside an egg or directly near it, I would strongly encourage you to take the specimen to your nearest paleontology related museum or university. If it does have embryonic remains in or near, then the specimen is invaluable to science. The presence of those tiny remains allows for the next question to be asked.
Do we know who laid this egg? Which particular dinosaur?
Most likely no, there are some wonderful exceptions though. Several ootaxa (eggshell type) are known to the dinosaur genus or family they were laid by. Here are some examples of eggs and eggshell which were linked scientifically to a particular dinosaur from embryonic remains.
Dinosaur or family and its known egg type, oogenus or oofamily. This list is not comprehensive as new discoveries and revisions are made every year.
Allosaurus sp. known to Preprismatoolithus coloradensis. (This is debated)
Beibeilong (Oviraptor) known to Elongatoolithidae.
Citipati (Oviraptor) known to Elongatoolithidae. (See the picture above)
Gobipipus (Avian) known to Gobioolithus minor.
Heyuannia (Oviraptor) known to Elongatoolithidae.
Hypacrosaurus (Hadrosaur) known to Spheroolithus oosp.
Lourinhanosaurus (Theropod) known to cf. Preprismatoolithus.
Maiasaura (Hadrosaur) known to Spheroolithus oosp.
Oviraptorid known to Elongatoolithidae.
Therizinosauroid (med to large theropod) known to Dendroolithidae.
Titanosaur (Sauropod) known to Megaloolithus patagonicus.
Troodon (small Theropod) known to Prismatoolithus levis.
Generally, be wary of any claim that an egg was laid by a certain dinosaur!
Additional information:
http://www.ucmp.berkeley.edu/science/eggshell/eggshell3.php
What groups of dinosaurs do we have eggs for?
The vast majority of eggs are from non-avian theropods. This group includes dromaeosaurs (like Velociraptor), allosaurs, and tyrannosaurs. We also have eggs from Mesozoic aves (birds), hadrosaurs (duck-billed dinosaurs) and sauropods (long-necks). It is worth noting when we say that the majority of eggs are therapod we mean it. Around 61% of the eggs found globally are therapod and between 41-64% are maniraptorans (birds and their closest non-avian dinosaur relatives). For the others the numbers are much smaller: 7% are sauropods, 13% are ornithischians (hadrosaurs and relatives) with 19% still unknown and that is no yolk.
Here is an example of a clutch from an oviraptor, elongated eggs are typical of many theropods:
Pic from The Zuhl Museum
On the non-dinosaur side of things, we also have eggs from turtles, crocodiles, lizards, and pterosaurs (flying reptiles).
There are several groups of dinosaurs who have no egg representation in the fossil record yet. Despite many people trying to find them, there are still no ceratopsian (horned dinosaur) eggs. There are no ankylosaur (armored dinosaur) or stegosaur (spiked/plated dinosaur) eggs as of yet either. This could simply be due to bias in the fossil record but there also could be other factors. Perhaps, it is a case like the ichthyosaur (marine reptile), which gave live birth, unlike most reptiles that lay eggs. Most of us are familiar with the platypus in the mammalian world, which lay eggs despite being a mammal. Maybe some dinosaurs did not actually lay eggs. Now that would be an eggciting discovery!
Below one can see how similar clutches are for two very different types of hadrosaurs.
The above is a rather typical egg clutch for a hadrosaur with spherical shaped eggs. Some of these eggs had embryonic remains which allowed them to be identified to a dinosaur. In this case they were narrowed down to within the lambeosaurinae subfamily but sadly could not be narrowed further. Pic from Museum of the Rockies
Clutch of another hadrosaur, the good mother Maiasaura. Again, the eggs are spherical and embryonic remains allowed the eggs to be linked with Maiasaura. Pic from Museum of the Rockies
The great identification mistake:
Now that it is abundantly clear the only way to link a dinosaur and an egg is with embryonic bone. Why is that? Surely there must be other ways to ID who an egg is from. Well, let me share the story of poor Oviraptor, who was wrongly accused of stealing eggs.
When the first Oviraptor was discovered, the skeleton was not alone. Underneath it was a clutch of eggs. At the time there were no embryonic remains in these eggs, so it was assumed that the strange looking animal was, in fact, stealing the eggs from Protoceratops, hence the name oviraptor meaning “egg thief.” Later, not far from the original site, another nest was found, this time with an almost perfectly preserved embryo. The embryo was clearly of that of an Oviraptor to be eggs-act. So, with both discoveries, paleontologists determined that Oviraptor was actually a brooding dinosaur much like birds today.
This story is an eggcellent example of science improving upon itself and the need to be careful with assumptions. Paleontology is an ever-changing field, which constantly works to improve our understanding of the prior natural world.
A common incorrect identification nowadays is that of “Tarbosaurus eggs.” Tarbosaurus is very similar to Tyrannosaurus rex, however, it lived in Asia. Among the largest of eggs ever found, were two measuring 11 cm (4.3 in) wide and an amazing 60 cm (24 in) long. The elongated shape meant they were probably from a large theropod and so were thought to be from Tarbosaurus. Scientifically these eggs are the oogenus macroelongatoolithus. Based on detailed analysis, these eggs most likely are from a large oviraptor and not Tarbosaurus. Alright, so then how are eggs differentiated and how without embryonic bones would an egg likely be from an oviraptor?
How are eggs distinguished from each other?
We went over how to link a dinosaur to an egg, what about one egg to another or finding differences between eggs? Well, there are a few different ways, one is the surface of eggshell. Many eggs have different textures but surface texture can be eroded or altered so cannot be used alone. Thickness and porosity of eggshell can be measured and provide solid data points for comparisons. Two of the best techniques for examining eggshell are with the use of SEM and thin sections. A scanning electron microscope (SEM) is a very powerful microscope, which can view objects in eggstreme detail. Petrographic thin sections are tiny slices of a rock so thin that light can actually pass through it. Both SEM and thin sections allow for the tiny details of eggshell to be visible, meaning unique traits, variations, and similarities can all be seen. Below are two types of eggshell, how many differences can you spot?
A thin section of hadrosaur eggshell, there is only a single continuous layer.
Pic from University of Calgary
A thin section of oviraptor eggshell, there are two distinct layers with the arrow showing the point where both meet.
Pic from University of Calgary
On thick eggshell, the cross-section view can often show many details otherwise too small to see. Below is Faveoolithus eggshell, which is large enough to show the internal structure of the shell itself.
Pic from Montana State University, taken by P. Germano
Naming:
Dinosaur eggs, much like actual dinosaurs, are named following a convention with information in the name, and normally an honor to an individual or location where it was discovered. As already covered, naming uses a system of parataxonomy and with eggs, this is called ootaxonomy.
Using the method covered above, similarities and differences of eggshell can be identified. Based on these similarities and differences, eggs can be grouped. Some of these groups are associated with a type of dinosaur. As already covered, from embryonic remains or other methods an animal can be linked and associated to its eggs. Sometimes eggs can be grouped based on similarities yet there are no ways to associate them with a dinosaur, so these are listed as unknown. An egg group being associated to a type of dinosaur does not mean all eggs within the group are exclusive to that single type of dinosaur. Some eggs were named prior to the naming convention being established or do not fit any of the known groups, as such these have a truly unique name. That said, most eggs fit one of the following:
Name- dinosaurs associated
Sphero- Hadrosaurs
Ovalo- Unknown
Faveo- Unknown (Could be sauropods)
Megalo- Titanosaurs
Dictyo- theropods
Dendro- Therizinosaurs
Elongato- Oviraptors
Prismato- Troodontids
Egg and dinosaur associations, from top to bottom, Elongato- with Oviraptors, Sphero- with Hadrosaurs, Prismato- with Troodontids, Dictyo- and similar eggs from unknown theropods. Pic from the Royal Tyrrell Museum
What time periods do we have eggs from?
Nearly every egg from the Mesozoic is from within the Late Cretaceous. One study found of 238 eggs examined, 225 were from the Late Cretaceous, 10 from the Early Cretaceous, 2 from during the Late Jurassic and a single egg from the early Jurassic. Since then more eggs have been found, yet the trend holds. A likely explanation for such massive bias would be the Late Cretaceous is more recent so eggs from then are more likely to be preserved and undergo less alteration.
Did an egg hatch?
The hatching question is a difficult one to answer scientifically with most egg specimens, of course, a nearly complete egg is likely unhatched. Much of the strength in eggs comes from their shape and this means once there is an opening in the shell that strength is lost. There are many ways for an egg to break, one of which is the baby breaking out, but many of the broken eggs we find may have yielded no baby. The term unhatched and failed are often used interchangeably but the term failed is preferred as “unhatched” which implies the egg was fertilized and had a real chance. It is possible and likely probable that no fertilization was the cause for many eggs to not hatch.
An overview of the different ways an egg can be filled. From Mueller-Towe et al. (2002)
Nest?
For as rare as eggs are, finding an egg clutch within a sedimentary structure is many times rarer. There have been several sedimentary structures found around egg clutches, which were interpreted as nests. One of the most interesting of these is a “U” shaped structure which looks similar to a horseshoe, see the picture below. In the center of this “U” shaped structure was a clutch of Troodon eggs. It is possible many nests were constructed like modern bird nests, with sticks, straw, leaves and other such material. This material in nest building, unfortunately, means they would most likely not preserve.
Possible nest structure for Troodon, tape measure equals 1m (39in) and the white plaster jacket is covering a clutch of Troodon eggs. Modified from Varricchio et al. 1997
How can we tell what happened to an egg and the nest?
By studying modern nests, it was found eggshell fragments tend not to travel very far while remaining in large concentrations. This means when a large grouping of eggshell fragments are found, it is unlikely they have moved much. Modern eggshell fragments can be found in ratios of concave up vs concave down based on what happened to the nest. For example, if a nest had a predator come and eat eggs, the eggshell would be concave up vs down in a ratio of about 70:30, sometimes 65:35. Obviously, if the eggshell fragments are moved then ratios will not work, but again, where high concentrations of eggshell are found, there was little to no movement. The ratio technique is still in the early stages of being applied to nest from the Mesozoic so in time there may be more information.
The Emu eggshell above is concave-up. Pic by P. Germano
The Emu eggshell below is concave down. Pic by P. Germano
In both pictures, different layers of the eggshell can be seen and such layering indicates the eggshell is from a theropod, in this particular case, an avian.
Where in the world are dinosaur eggs found?
Eggs are extremely rare and there are only a select number of places where they have been found so far. Eggshell fragments, on the other hand, are actually rather common and can be found in many formations. One main reason eggshell is relatively abundant compared to complete eggs is that a single egg when broken can become dozens of fragments. Geographically eggs so far were found in Argentina, Canada, China, Columbia, France, Great Britain, India, Kazakhstan, Mongolia, Peru, Portugal, Romania, South Korea, Spain, Switzerland, the United States, and Uruguay. Within Canada, eggs are exclusively found in Alberta. Within the USA, eggs have been found in Colorado, Idaho, Montana, New Mexico, South Dakota, Utah, and Wyoming. The vast majority of eggs are found in Asia.
Additional information:
http://www.ucmp.berkeley.edu/science/eggshell/eggshell4.php
Did dinosaurs care for their young?
It seems that many dinosaurs did in fact care for their young. Evidence for this has been found on multiple continents. There is still debate over the type and amount of care the parents may have provided. There are two major variations in care being debated, and these come down to whether the offspring were altricial or precocial. See the list of terms near the end of this guide for definitions. One possibility is that a group of adults would use cooperative breeding to care for a clutch, this is basically the village raising a child approach. With theropods, in particular Oviraptor, the presence of adults on eggs does support incubation and possibly even brooding. Hatchlings have been found within a nest and could have died there for many reasons, brood reduction and siblicide are both entirely possible. Given the diversity of dinosaurs, it is likely different dinosaurs provided varying levels of care for their young.
Modern example showing a female crocodile providing care:
Modern example of a spoonbill bird raising young:
Some dinosaurs such as the sauropod titanosaurs, likely did not care for their young but rather used the same strategy as sea turtles. A large group of females would lay hundreds of eggs at once to overwhelm the predators and just by sheer numbers allowing some of the babies to live to adulthood.
Are there any diseases or mutations of eggshells?
Yes, we have paleopathologies found in eggshell. Paleo meaning ancient and pathology being the study of diseases, so paleopathology is the study of ancient diseases. One of the more common is where two or more layers of eggshell overlap in a way where the pores no longer pass through the entire shell, this reduces the amount of oxygen an embryo can receive. Too many of the pores being misaligned can be fatal.
What color were eggs?
One of the most recent breakthroughs in egg research is an ability to determine colors present within fossilized eggshell. Interestingly, from the eggs so far examined there seem to be many colors and patterns. With this being rather new to the field, not many eggs have been tested plus there is likely some error and bias. Even so, there are remarkable results. Some eggs were simple, just white. Some were speckled. Many were dull earthy colors, while others were green and blue. Given their close relationship, it is logical to assume dinosaur eggs could show any variations of what we see from either crocs or birds. Modern crocodiles have white eggs whereas modern bird eggs range in color and pattern. Interestingly, even within the same bird species there is a range in color, so it is entirely possible dinosaur eggs from the same species also vary in color.
Three modern chicken eggs showing variation in colors and size.
From Wikimedia Commons
What is working with eggs like?
Fieldwork:
The basic process of removing eggs from the ground is very similar to that of removing fossilized bones. The approximate size of an egg is figured out and then the area around it is trenched until a plateau is formed. Next, a plaster jacket is made encasing the plateau. The bottom of this is removed until the whole thing can be “popped.” After which it is flipped and then is ready to be brought back to the museum.
An egg at a new nesting site just after I uncovered it. Pic from the Two Medicine Dinosaur Center
Jacketing an egg at Egg Mountain in Montana. Pics by D. O’Farrell.
To find small fragments of eggshell and embryonic bones, removed rock is often sifted. Since they are so small—and also a rock surrounded by rocks—many times until sifted, the tiny bones or eggshell are not visible.
Sifting for eggshell, here I am showing Paleontologist Barbie an example eggshell fragment. Pic from Coffeewithhallelujah
After viewing the example fragment, my esteemed colleague Paleontologist Barbie was able to find an eggshell fragment. Can you find the piece of eggshell below?
Pic from Coffeewithhallelujah
Preparing and reconstructing an egg:
Eggs tend to be more tedious and require more patience than normal prep work. Eggs are not that difficult to prepare, however, to an even greater extent than bones, they are very unforgiving. Reassembling a fossil bone after a mistake is not necessarily easy, however it is normally possible. The same often cannot be said for fossilized eggs. If you ever want to try and reconstruct a dino egg, just save the last chicken egg after cracking it and then try to reassemble. Remember, chickens are dinosaurs and their eggs make a decent modern analog to a classic theropod egg.
Eggs in context- The Two Medicine Formation:
To bring us all the way back to the beginning, what is the importance of studying eggs? Why bother? The primary geologic formation I have spent the last seven years working in is the Two Medicine and in terms of eggs, it is the most significant location in North America. One newly discovered nest I am fortunate enough to have an ongoing role in excavating and scientifically describing. From eggs and embryonic remains, the ecosystem of the Two Medicine is relatively well known compared to nearly every other formation. In terms of paleoecology, nesting sites show where adults felt safe and secure with enough food, water, and other resources. Within this formation was true evidence for parental care, particularly care in the form of nurture similar to birds. Behavior is nearly impossible to deduce from the limited fossil record, yet the care for young is strongly supported thanks to discoveries in the Two Med. Three dinosaurs from the formation have been linked to their eggs, Hypacrosaurus, Maiasaura, and Troodon. It may not seem impressive but three dinosaurs with embryonic remains is a truly remarkable find and incredibly rare. Even now, after over forty years of study, the Two Med continues to surprise with new nesting sites.
Read about how the Two Medicine and Maiasaura was discovered:
Additional information:
http://www.ucmp.berkeley.edu/science/eggshell/eggshell_case1.php
https://www.nps.gov/articles/mesozoic-egg-mountain-dawson-2014.htm
https://serc.carleton.edu/research_education/mt_geoheritage/sites/augusta_choteau/paleontology.html
http://www.georgialifetraces.com/2014/07/15/tracing-the-two-medicine/
http://www.georgialifetraces.com/2014/08/04/fossil-visions-in-the-two-medicine/
Dinosaurs as living animals:
Eggs allow us to see these animals as just that, animals. There is a reason many feel sad when seeing a baby dinosaur still in its egg, yet the same sadness tends to not be shown for adults. Why? The poor baby was deprived of an actual life and it is easy to relate. When covering a natural disaster, one goal of reporting is to humanize the story. In a similar way, when reporting on dinosaurs, it is important to try and do the same. Eggs allow us to come far closer to dinosaurs as true animals than I feel we ever will through bones alone. Eggs and reproduction give a window into the lives of these wonderful animals. When trying to describe what separates something living from an inanimate object, the ability to reproduce is used as a major criterion, therefore making it one of the most important aspects of dinosaurs to study in detail.
Some Relevant Terms:
These typically are used for modern birds and the classic theropods.
Altricial: A developmental classification where at hatching, the offspring are relatively immobile, lack feathers or down, have closed eyes and are completely dependent on their parents for survival. Altricial birds include herons, hawks, woodpeckers, owls, and most passerine songbirds.
Brood (n): The offspring of an animal which are hatched or cared for at one time.
Brood (v): To sit on and keep warm.
Brooding: To sit on and keep offspring warm when they cannot maintain their own body temperatures.
Brood reduction: A reproductive strategy where the female lays more eggs than can be cared for and raised. The smallest and weakest of the brood typically starve or are killed by siblings.
Clutch: Total number of eggs laid by a female in one nest attempt, often 3 or more.
Conspecific: Of the same species.
Cooperative breeding: Breeding system where non-parental adults assist other breeding pairs (usually their own parents) to rear offspring, instead of dispersing from the nest or breeding themselves.
Incubation: The process by which parents keep eggs at the proper temperature to ensure normal embryonic development until hatching. In most cases, birds sit on eggs and transfer their body heat through a patch of skin known as the brood patch. In many species, only the female incubates; in other species, both males and females incubate. Less common is where only the male incubates.
Precocial: Offspring are capable of a high degree of independent activity immediately after hatching. Precocial young typically can move about, have their eyes open and will be covered in down at hatching. They are generally able to walk away from the nest as soon as they have dried off.
Siblicide: The death of a young animal usually as a result of fighting with siblings over food, common in years when food is in short supply.
Further reading and information:
https://www.amnh.org/our-research/paleontology/about-the-division/more/fossil-identification/dinosaur-eggs-fossil-identification
http://www.ucmp.berkeley.edu/science/eggshell/index.php
http://www.ucmp.berkeley.edu/science/eggshell/eggshell_hirsch.php
http://www.ucmp.berkeley.edu/science/eggshell/eggshell5.php
https://feederwatch.org/blog/raptors-make-good-neighbors-hummingbirds/
Images:
University of California Museum of Paleontology: http://www.ucmp.berkeley.edu/
Yang et al. 2018: https://doi.org/10.7717/peerj.5144
Montana State University: http://www.montana.edu/
Two Medicine Dinosaur Center: http://www.tmdinosaurcenter.org/
Royal Tyrrell Museum: http://tyrrellmuseum.com/
Museum of the Rockies: https://museumoftherockies.org/
The Zuhl Museum: https://zuhlmuseum.nmsu.edu/
Dr. Tony Martin: http://www.georgialifetraces.com/
Mueller-Towe et al. 2002:
https://www.researchgate.net/publication/260391508_Hatching_and_infilling_of_dinosaur_eggs_as_revealed_by_computed_tomography
University of Calgary
Hadrosaur eggshell: https://www.ucalgary.ca/drg/imagesort/00S000500
Oviraptor eggshell: https://www.ucalgary.ca/drg/imagesort/00S001300
Varricchio et al. 1997:
https://www.researchgate.net/publication/232793785_Nest_and_egg_clutches_of_the_dinosaur_Troodon_formosus_and_the_evolution_of_avian_reproductive_traits
Coffeewithhallelujah: http://coffeewithhallelujah.blogspot.com/2015/07/paleontologist-barbie-at-two-medicine.html
Wikimedia Commons
Citipati: https://en.wikipedia.org/wiki/Citipati
Chicken eggs: https://en.wikipedia.org/wiki/Egg_as_food
List of open access egg related papers:
Thanks to the late Joe Gallo for this wonderful list.
Disclaimer:
For legal purposes, it should be noted links to an institution does not constitute endorsement by the respective institution and pictures are used here for educational purposes only. All rights belong to their respective owners.
From the 2018 SVP meeting, my poster, which was a presentation on new dinosaur eggs. Pic from the Two Medicine Dinosaur Center
Many thanks to J. Cozart and L. Murphy for writing some sections as well as edits. Thanks to D. Lawver, Ph.D. for reviewing the information presented. I especially would like to thank @Fossildude19 for assisting me and additionally thank these members for input and suggestions: @Troodon . @Seguidora-de-Isis . @HamptonsDoc . @-Andy-
Eric P.

The Basic Dinosaur Egg Guide
Many people often mistake a concretion for an egg, to help clarify what is a concretion, and what is a real egg, here is a guide.
A quick overview with examples:
How to spot a concretion:
How are they different from eggs?
A concretion is a rather common rock made of tightly compressed minerals. Typically, concretions are a smooth sphere or oval with little to no surface texture or just a few bumps. Often nearly a perfect sphere, sometimes more of an oval. In a concretion, there is no eggshell. If you cannot see eggshell then you do not have an egg. If it looks the same shape as modern egg, such as from chicken then you do not have an egg. Concretions may have fragments breaking off and these will tend to be smooth on both sides. They tend to be dull earthy colors with a different composition in the center, as seen by a change in color. A different color in the center normally means you do not have an egg. Often circular bandings can be seen around exterior of concretions. Sizes of concretions range from just an inch, or a few millimeters, up to more than 10 ft (3 m). Egg sizes, along one side, range from just an inch or a few millimeters and top out at around 8 in (20 cm). If you find an oval or round shape, which is larger than 8 in (20 cm) along a side then it is probably not an egg.
For more information on concretions:
https://www.priweb.org/index.php/education/education-projects-programs/earth-101/concretions
http://tumblehomelearning.com/geologists-find-largest-dinosaur-eggs-in-the-world-another-fraudulent-fossil/
https://en.wikipedia.org/wiki/Concretion
In video form: https://www.youtube.com/watch?v=B5IoyLEwkMY
Example of concretions, these three were incorrectly given an ID as “dinosaur eggs” however they are clearly not:
From Tumblehome Learning, link above
Pseudofossils:
There are some pseudofossils, which can have a similar appearance to an actual egg, right down to seeming like there are bits of eggshell.
This pseudofossil does look similar to an egg and even seems to have eggshell, however it is not an egg and is actually geologic. The surface ranges too much in texture and composition. Pic from Montana State University, taken by P. Germano
Trace fossils:
Many times, an actual trace fossil can be mistaken for an egg, common examples of this are pupa cases and cocoons. As one can see below, they do tend to have an egg-like shape and are yet another perfect example of why shape alone should not be used when trying to identify eggs. The three below are important trace fossils, just not eggs.
Pic by Tony Martin, Ph.D.
How to spot a real egg:
The best and only true sign you have an actual egg is eggshell actually being present. Eggs come in many shapes from a semi-rounded, elongated oval to a perfect sphere and many others. Shape is not a good indicator of an egg. It is useful but only when combined with other details. Eggshell often has surface ornamentation that gives it a unique texture which can be seen by the naked eye or with a hand lens. There are many such ornamentations and they are used to help distinguish one egg type from another. On the surface look for little bumps, ridges with valleys, river channels, and similar textures. Individual fragments of eggshell are rather common in some geologic formations so be on the lookout for a larger grouping of eggshell.
From University of California Museum of Paleontology
Also read:
http://www.thefossilforum.com/index.php?/topic/59654-dinosaur-eggs-lowell-carhart-guide/
Examples of real eggshell:
Example of eggshell fragments:
An eggshell fragment from Maiasaura, which is the oogenus Spheroolithus oosp. Pic by W. Freimuth.
Examples of real eggs:
A clutch of Troodon formosus eggs, which are the oospecies Prismatoolithus levis. Pic from Museum of the Rockies
Do I have embryos inside this egg?
Most likely no. Embryonic remains are extremely rare within eggs, and you add that with the rarity of eggs to start and it is a remote possibility. No fossilized yolks have been found and since they are soft tissue, it is near impossible for any to fossilize.
I still think this is an egg!
If you still think you have an actual egg, then please start a thread. Take close detailed pictures with something for scale such as a ruler and provide all the information you can about it--like where it was found. Good pictures will help greatly with a proper and correct ID.
Below is an example of how to best photograph an egg or eggshell. There is clear lighting, a background which is clearly different than the eggshell in question and a scale bar. Lights can be as simple as a desk lamp; a scale bar can just be a ruler and the background can be very simple, in the example just a paper towel.
Megaloolithus egg. Pic from Montana State University, taken by P. Germano
If you would like to learn much more on eggs, here is the advanced egg guide which goes in depth. Also, see the advanced guide for sources.
Eric P.

Ok, I went looking for fossils in Renton, Washington state. I also went to Tukwila Washington (supposedly there are plant fossils here.)
I found some things and maybe anyone could confirm if they are indeed fossils or something else. I'm not aiming for species of genus, the quality of these are not to that level, BUT if you have an idea, let me know. Thanks all. (I'm going to do kind of a dump here with all my findings.)
Fig. A: Found in Green River Tukwila Washington. Not sure just picked the piece up about 1 1/2 inches long.
Fig. B: Found in sedimentary rock in Renton Cedar river park. (people have found fossils here before) The picture of the boulder shows where the rock / fossil was lodged into it.
Fig. C: I have no idea, it jumped out at me at Cedar River on the river bank next to a natural cut in the sediment.
Fig. D: I believe this is old Carbonized wood or something like that but I'm so amateur I probably don't know what I'm talking about. It was found in the sediment (in the picture you can see it sticking out of rock). The Geologic map says Renton is in the Eocene time period but I know wood takes 300 million years to carbonize (So I read) Anyways if you could tell me how this got so deep in the sediments and maybe its age that would be great. (the sediment was on the side of a cliff so it wasn't someone's campfire unless they broke gravity.)
Fig. E: Again, not sure. It feels like carbon but maybe with bark or something on it.
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The last few images I couldn't take home because they were too huge
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Fern maybe: I found this in Renton WA by Green river.
Carbonized Log Maybe: I found this streak of charcoal looking substance imbedded in a rock and I cant get it out but it is indeed deep in the rock. You can see on the side that it goes all the way through.
Tukwila Maybe Plant: Probably the only fossil I found so far. I have my best bet on this one. No idea what it truly is.
Dash Point Leaf?: At Dash point Tacoma Washington I found this chunk of clay with a deciduous looking leaf shape but I did not take it home with me. A lot of this clay had black splotches on it and it was probably only a coincidence.
If you made it this far holy cow I'm sorry for just dumping but anything helps. THANK YOU!

I dont have a lot of room in my fossil/computer room,, so when I start to sell off some things,,,,,,,,,, they get in the way. Does anyone else have this problem? Its not a bad problem so maybe I should just quit complaining. or get a bigger room?
RB

I just wanted to know what feilds I can work in in the future. I love picking up rocks and fossils, Is there some kind of mix between paleontology and geology? Could I make a living on this kind of job? I am hoping to study in austrailia some day.

Hi everyone.
I am completely inexperienced in this. I dont even know if I have actually found a fossil. I live in the Karoo and found the attached rocks on one of my mountain climbs. There seems to be a layer of this rock about halfway up and I am sure there are plenty more. If you can advise me. I apologise for the quality of the pictures and hope you can make them out. Thank you so much

Last October I visited Dave's Down To Earth Rock Shop located in Evanston, Illinois and I put together a picture heavy post in the "Trip To the Museum" section of the Forum. At that time I took pics of a lot of great fossils from different locations and all time periods, if you have not seen that post, you should take a look at it, you would be hard pressed to find this quality of fossils in the largest institutions.
Today I picked up my grandson and we drove the 14 miles from his house to Dave's. I usually use a scale cube when taking pics of my fossils, but decided to use my 5 year old grandson instead.
As I stated above, Dave's is such a great store to purchase Rocks, Minerals and Fossils- but it also has a fantastic "Prehistoric Museum" in the basement. I have been to many Fossil Stores across the US and I have never been to one that can compare to Dave's or even come close. If you are ever in the Chicagoland area you need to stop by this place and I guarantee that you will leave drooling.
I am going to break this picture heavy post into TWO sections. The First section will contain pictures of some of the best, if not the best, of what Mazon Creek concretions can hold. In this section you will also see THREE HOLOTYPE Mazon Creek Fossils- one after Dave, one after his father and the other after his mother. The Second section will pics of some of the fossils that are for sale at the store.
MAZON CREEK-
The first fossil that I will show is one that I personally found about 25 years ago while sitting on the ground near "Tipple Hill' at Pit 11. This is a rare fossil and the only Mazon Creek fossil that I have ever sold, I really wish that I never did, but it can now been seen but the countless people that visit Dave's.
Here are the Three Holotype Fossils-

Hello everyone, I am in desperate need of help with a huge debate I have been having with a friend over fossils preserved in ironstone concretions. From some of what I had read to some advice from other members I it possible to find vertebrate bone among shells and other mollusks preserved in an ironstone concretion. Whether it leaves a trace of the organism, morphs the organic material into the structure of the iron concretion through the decomposition with preserving, or whatever else it may be it seems to be possible.
So recently I have hunted a place known to have recorded marine cretaceous shell and other mollusk found in ironstone concretion as well as cretaceous plants in shale, it seems like not to vast of enough study has been done there only from what I know, but since no vertebrate material had yet been discovered there though there can maybe be the possibility.
I found these two particularly distinct pieces in iron concretions that exactly mimic the scute structure of soft shell turtle and croc in my opinion, I know how iron concretions are famous for leaving psuedofossils and such but these two pieces look way to exact and since its possible for shells and mollusks to preserve why not scutes?
So I am here looking to end this debate, I'm looking for your opinion, can these be labeled as fossils, traces, etc? Or are these among some of the world's best iron concretions and nothing more. Your input especially if you are very experience in this subject would be tremendously appreciated.

Hey everyone,
This is my second post hopefully I can get some answers on these!
I found these in a town called Tunkhannock in Northeastern Pennsylvania in part of a mountainous area. They were just in some shale I was breaking up. Any kind of research I’ve done says there’s really not much for fossils in that area. Any ideas??
Thanks in advance friends!
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Hi guys,
I am not even sure if this is the correct place to ask, but lets give it a try.
This past weekend I visited my hometown, Tampico in Mexico (right in the center of the Gulf of Mexico). It is a beach town, and it also has a big River that goes into the ocean so it has been a major port for many years. Recently the local governmet decided to do some maintenance on the beach promenade. A bunch of big rocks were moved from the Tamuin area (112 kms west from Tampico) and basically dumped along the promenade to contain the waves. The rocks have many shapes on their surface and different colors. I am extremely curious to find out what they are, but being an accountant I am absolutely clueless.
If anyone knows what these are or can direct me to another forum where I could ask please please lemme know.

The person who owned my home before me left quite a rock collection around my yard. I seriously thought this was a cow patty when I first saw it. But upon closer examination it was just a weird, oyster shaped rock in a grey limestone like clay. It has shell casings around a few of the ridges and seems to have an oyster like shape. It also has small clear crystals that crust some of the ridges and crystalline matter mixed into the grey sludge clay its encased in. It weighs a lot, so I didn't think this was a fossil, but a friend who has more experience with fossils thinks its a fossil. I might upload some better pics later after I charge my camera.

Hey guys,
I’m currently in Dallas for work and was walking home when I saw some weird rocks by the side of the path. Two of them put me in mind of coprolites, and one like a bit of bone or petrified wood. I’m very open to these being nothing, too. Any ideas?
Thanks!
Robbie

Over the past couple weeks I have seemed to find multiple variations of petrified wood. In this picture the top few pieces were all found in the same area and some of the smaller pieces that I found have little crystals throughout them (like the one in the top of this image). The piece I found on the bottom confuses me because it resembles wood but also has a mineral/rock look to it. I have read into agatized petrified wood but I still don't know much about that process. In the past I have found very large pieces of what I believed to be petrified wood but the majority of the piece resembled a crystal. Unfortunately I don't have those with me but will post a picture of them when I get home. Any info and help on the subject would be appreciated. Also sorry the picture posted weird. When i refer to the top I mean the right side of the image. Thanks, Nic

Hello! I'm new to this website and I'm wondering what interesting geological things and fossils I can find in Northern Illinois. I'm new to geology and fossils so any tips/education would be welcome! Thanks!

I have 11 rocks that I believe contain fossils. Is there anyone on here who can verify if these are indeed fossils? These rocks were obtained years ago in Texas while oil drilling. They were found at approx 50-60- feet below the ground.

After visiting the MAPS Show yesterday in Iowa City, I decided to stop by a small show that was held in a Western Suburb of Chicago. It was the 50th Annual Des Plaines Valley Geological Society Show and it was the first time that I have attended. It is a very small show that is really geared towards rocks, minerals and jewelry, but there was one vendor that I saw there that had fossils. She had various items for sale, but the prices were quite high for many of the items ( i.e. 1" portion of a Spinosaurus tooth for $150.00), but being a local show, I do like to purchase 1 or 2 items to help the vendors, so I bought a couple fluorescent minerals for my 4 year old grandson and a small bird bone in Tar Matrix (Rancho La Brea, CA), though I think it may have come from Maricopa Brea, CA.
Like other shows, they had a couple of displays , door prizes and silent auctions. If you live in the Chicagoland Area ans you have nothing to do tomorrow head out to Des Plaines and check it out- the information is on The Fossil Forums Calendar.
Here are some pictures from the show:

“The 38th annual Geodeland Earth Science Clubs, Inc.’s (GESCI) Rock, Gem, Mineral and Fossil Show will be held Saturday-Sunday, March 10-11 in the Western Illinois University Union Grand Ballroom.
The show is open from 10 a.m.-6 p.m. Saturday and 10 a.m.-5 p.m. Sunday. Admission and parking are free, but a free-will donation is used to obtain feature displays for each year’s show.
This year’s theme is “Digging the Past: Fossils from Around the World,” and highlights a program by WIU Assistant Professor of Geology Thomas Hegna.
LINK

I enjoy all types of fossils, rocks, & skulls. I've never hunted my own (except for hanging out in rock shops in Colorado!). I live in Chandler, OK & would love to learn about where I can go to hunt for my own fossils. Just an occasional outing once or twice a year. Any ideas?

Hey yall,
I'm new here so not sure if this is the appropriate place to ask this. Wasn't sure where else to ask. I have a few rocks(septarian nodules) some large, some small that I need to get cut. The largest is about 12" long and 6" wide. Does anyone know how or where I can go about getting these cut? I've thought about using a wet tile saw but I have a feeling I would need a rather large one. I don't want to spend money buying one as I would only need it for about 5-6 rocks, but would be willing to pay someone if need be for the services to cut them. If this is the wrong place to ask, could someone direct me in the right direction? Thanks a bunch!

I came across a blog talking about Mineral Hill near Liberty Reservoir in Carroll County and thought about taking my son out to look for some neat samples in the old mine dump piles since it's only 30 minutes away. I was wondering if anyone else knew of other places in central Maryland or even the southern half of Adams county PA that are known for interesting rocks and minerals. I know quarries let geological clubs collect on occasion. Sorry if this needs moved to the rock & minerals section or geology section, I thought since I was interested in a specific location this would get better results.